1. Field of the Invention
The invention relates to a flow line monitor pilot valve assembly which automatically activates a spool valve assembly to block and bleed control fluid for manipulation of a downstream valve mechanism to closed position when abnormal pressures in a monitored fluid are detected. The spool valve is manually or mechanically manipulatable at any time to open or close the downstream valve.
2. Description of the Prior Art
As a safety precaution, oil and gas wells are required to contain one or more subsurface safety valves, which are typically of ball-type construction and are manipulated between open and closed position by variation of hydraulic control pressure. The safety valves are manipulatable to closed position when detection devices immediate the well respond to an unfavorable condition, such as an increase in temperature, indicating a fire, or by abnormal increase or decrease in well production flow, indicating a flow line plug or rupture. The monitoring devices transmit the abnormal signal to a device which causes automatic loss of hydraulic control fluid to the safety valve, and the safety valve is manipulatable to closed position.
Pilot relays heretofore utilized have incorporated pressure unbalanced poppet-type valving mechanisms because spool valves having very close tolerance metal sleeves result in high friction being encountered across the valve as the head is shifted with respect to its seat. Thus, it would be desirable to have a valving mechanism which does not encounter friction as the head is moved relative to the seat.
Some prior art pilot relays are pressure unbalanced and require pneumatic signal to allow hydraulic pressure to the downhole safety valve. In these systems, the pneumatic source is typically tapped from the well, so that when the well is shut in, there is no source of control fluid to reopen the valves. This, in turn, has required utilization of mechanical defeat mechanisms or hand pumps to activate the system to manipulate the valve again to open position. These start-up techniques, if not mechanically released, will defeat the entire safety system.
Valving mechanisms heretofore known and utilized have required the incorporation of numerous valves and complicated circuitry. The multiplicity of valves has been utilized to interface many sensing signals, usually at a minimum of one valve per signal. In these systems, manual valves are required to by-pass sensing signals for start-up. Additionally, other manual valves are required to shut down the system. Frequently, hand pumps or mechanical defeat mechanisms have been required to start up the systems. Not only are these valving systems complicated, but they are expensive, result in frequent service problems, and, because of their complexity, have a higher probable failure rate, and are thus unreliable.
Some prior art valving means have utilized spherical elements which essentially act as a valve head which is selectively movable onto and off of an adjacent seat by means of a spool element which is shuttled to manipulate a spherical element. For example. U.S. Pat. No. 2,574,335 discloses two sets of two ball elements each which are opened and closed at the same time in a fluid pressure motor device for control systems. The shuttle device contains a conical carrier surface manipulating a first ball on the conical or beveled surface to move an enlarged ball thereon between open and closed position within flow passageways.
U.S. Pat. No. 2,891,518 utilizes spherical or ball elements which are not normally free traveling or sealingly engagable upon a seat by differential pressure caused by fluid flow.
U.S. Pat. No. 2,967,544 also is typical of the prior art utilizing spherical elements as a valve head. This patent utilizes compressed spring elements and a mechanical manipulator to shift the balls between opened and closed position with respect to their ports. The spherical or ball elements are not carried by a spool which is shuttleable.
U.S. Pat. No. 3,007,492 discloses a pilot valve for fluid flow systems utilizing a spherical or ball element as the valve head. The ball elements are contained within a shuttleable spool element which is only shuttleable by exertion of a spring element in one direction. A piston head in a piston chamber is utilized to shuttle the spool in the opposite direction against the spring.
U.S. Pat. No. 3,053,279 discloses a directional valve containing a plurality of ball elements manipulatable by a spool to control flow from a second passageway to a first passageway. In one position of the spool, all of the balls are positionable on each of the respective seats. This valve is utilized to control flow from a second passageway to a first passageway, and flow therebetween is controlled by the positioning of a ball within the first passageway.
The present invention obviates the problems set forth above and differs substantially from the prior art. The present invention allows shifting of the spool element in response to detected abnormal pressure of a monitored fluid to block and bleed control fluid without affecting manual control capabilities. Additionally, the present invention does not require by-pass valves, mechanical defeat devices, or hand pumps for system start-up. Additionally, the present invention does not rely upon pressure unbalanced poppet-type valve mechanisms, but provides a bi-stable valve which tolerates exposure to high pressures. Additionally, the present invention permits easy manual or mechanical shuttling of the spool assembly at any time. Moreover, the present invention differs substantially from the prior art by utilization of a spool element containing spherical or ball means carried thereby which are selectively engagable onto and wipable off of their respective seats.
Other advantages of the present invention will be apparent from a reading of the Figs., the specification, and the claims below.